Low coherence broadband optical sources are required for optical imaging and optical sensors. Such sources are used for example in coherence domain optical tomography, some medical diagnostic technology such as Doppler velocimeters, remote sensors for detecting temperature, pressure, strain, etc., low coherence light source based fiber optic gyroscopes, fiber optic instrumentation, etc.
Such applications have very high optical light source spectrum width and shape requirements as well as power density of the main optical emitter or lighting device. For example, in optical imaging, the imaging resolution, defined by RES=f(.lambda.)*1/.DELTA..lambda., .DELTA..lambda. being the spectral width and f(.lambda.) a function depending on source wavelength, changes with the optical source bandwidth. Thus when the source spectrum is broader, the resolution is greater and more detail can be seen by the imaging system. In an optical sensor application, a greater optical emitter bandwidth means more sensors can be included in a single sensing system sharing the same optical source, and the whole sensor system cost can be lower since fewer optical emitters can be used.
The power level of the source is also of concern, since the sensor system loss budget can be greater with a higher power optical source. Total power of the source determines the imaging or sensor system loss that can be tolerated. Loss is caused by the high light scattering nature of the human tissue into which the light caused to penetrate. Higher power represents deeper penetration of the light into the tissue under diagnosis.
More importantly, the power of the source determines the imaging speed, which determines whether the source can be used to do in-vivo disease detection in hospitals and clinics.
In the case of fiber optic temperature or strain sensing, hard to reach regions where sensors (such as fiber Bragg grating based sensors) are introduced can introduce large losses, either due to long light transmission distances or due to fiber bending. Higher emitter power can increase the sensitivity of the sensor.
The spectrum shape of the light source is also important, particularly for optical imaging systems in which a quasi-Gaussian spectrum shape is required for clean and sharp image quality.